1. Field of the Invention
The present invention relates generally to installing a line in coiled tubing and more particularly to methods and apparatus for deploying fiber optics under pressure into a wellbore using coiled tubing.
2. Description of the Related Art
Coiled tubing is used frequently in various borehole applications. A typical configuration for the surface handling equipment for coiled tubing is shown generally in FIG. 1. The surface handling equipment includes an injector system 20 on injector supports 29 and coiled tubing reel assembly 10 on reel stand 12. The tubing is deployed into or pulled out of the well using an injector head 19. The equipment further includes a levelwind mechanism 13 for guiding coiled tubing 15 on and off the reel 10. The tubing 15 passes over tubing guide arch 18 which provides a bending radius for moving the tubing into a vertical orientation for injection through wellhead devices into the wellbore. The tubing passes from tubing guide arch 18 into the injector head 19 which grippingly engages the tubing and pushes it into the well. A stripper assembly 21 under the injector maintains a dynamic and static seal around the tubing to hold well pressure within the well as the tubing passes into the wellhead devices which are under well pressure. The tubing then moves through a blowout preventor (BOP) stack 23, a flow tee 25 and wellhead master valve or tree valve 27. A quick connect fitting is placed between the BOP and the stripper above.
It is routine to deploy coiled tubing into a wellbore under pressure. The following general procedure typically is used when running a coiled tubing string into a well. First the wellhead master valve 27 is closed to seal off the well and the BOP stack 23 is opened. Then the service end of the coiled tubing is run over the guide 18 and through the injector 19 and stripper 21, and a bottom hole assembly (BHA) is assembled onto the leading end of the tubing 15.
After the BHA is connected, the injector assembly is raised with the BHA extending from the bottom and lowered into the top of the BOP stack 23. Stripper 21 is bumped up on the stack and the quick union on the bottom of the stripper and top of the BOP stack 23 is made up. A pressure test is conducted with the wellhead tree closed and the coiled tubing open into the flow tee 25 at the bottom of the BOP stack 23 to pressure test surface treatment lines, wellhead connectors and flow control devices. The pressure on the coiled tubing system and control stacks is matched to the well pressure and the well is opened. The coiled tubing is then run into the well.
In some situations, it is desired to convey tools, sensors, or other apparatuses into a wellbore using coiled tubing. Coiled tubing is particularly useful for conveying such devices in highly deviated or horizontal wells. When the functionality of the tools, sensors, or other apparatus requires electrical communication the downhole device and the surface, it is known place a wireline cable within the coiled tubing.
Placing cable into coiled tubing typically involves unreeling the coiled tubing and installing the cable in the straightened tubing. One method involves unreeling the coiled tubing, hanging it in a wellbore, placing the cable inside the coiled tubing by gravity feed, and then reeling in the tubing with the cable inside. Another method involves unreeling the coiled tubing along on a long stretch of ground on the surface, attaching a pig to one end of the cable, and pumping fluid such as water into coiled tubing to propel the cable along the length of the coiled tubing as guided by the pig. It is apparent that the additional time and effort required to place cable in coiled tubing in these manners is operationally undesirable. Placing cable in the coiled tubing while the coiled tubing is spooled on the reel is preferable.
A few methods of pumping cable into coiled tubing while reeled are known. These methods generally involve injecting cable into the coiled tubing by pumping water or another fluid at sufficient flow into the reel of coiled tubing to propel the cable through the coiled tubing. Movement of the cable is resisted however by the pressure differential between the pressurized coiled tubing reel and outside ambient pressure at which the cable is provided, as well as friction forces at the interface where the cable enters the pressurized coiled tubing reel. In particular, the cable tension induced by the cable seal through which the cable must be passed into the tubing acts against movement of the cable into the borehole.
In general, mechanical means such as including a capstan with a pressure housing to direct the cable into the reel of coiled tubing as described in U.S. Pat. No. 5,599,004 have been used counteract the pressure forces resisting injection of the cable into the pressured coiled tubing. U.S. Pat. No. 5,599,004 discusses in passing the concept of placing an entire spool of cable inside a pressure chamber as an alternative configuration as this would eliminate the need for a seal. It discards the concept, however, noting problems with aligning cable with coiled tubing and controlling the cable insertion are expected, along with an unrealistically high cost for such a system. These impediments among others have prevented development of a pressured system for injection of cable into coiled tubing.
US 2004/0104052 describes methods for performing coiled tubing drilling using concentric outer and inner coiled tubings. In certain configurations, an electric wireline is provided inside the inner coiled tubing by using a second coiled tubing bulkhead.
U.S. Pat. Nos. 5,573,225 and 5,699,996, both incorporated herein in the entirety by reference, relate to an apparatus and methods for pumping cable into a coiled tubing using fluid and without using a mechanical device to pull the cable through the seal. These patents describe an apparatus and methods for passing a cable through a seal into a tube having a coupling in fluid communication with a fluid pump. Fluid is then pumped into the tubing at a rate sufficient to cause a drag force on the cable sufficient to equal or overcome the frictional force exerted on the cable by the seal and the differential pressure on the cable that would tend to force it back through the seal. The drag force causes the cable to move axially within the tube toward the end remote from the seal.
In placing wireline cable in coiled tubing, there are several advantages of a fluid flow system over a mechanical system that uses mechanical pulling or pushing to overcome cable tension. It is easier and less expensive as well as being safer and easier to control. The forces applied to the cable are low so the potential for damaging the cable during installation is less than when using a mechanical pulling device. In addition to installing cable in coiled tubing, fluid pumping techniques are also useful for removing cable from coiled tubing.
Several difficulties remain when providing wireline cable in coiled tubing. For example, managing slack in the wireline while it is interior to the coiled tubing poses operational difficulties. In addition, the presence of wireline in the coiled tubing reduces the available capacity for pumped fluids within the coiled tubing. Furthermore, the following process is known when using providing sensor or measurement apparatus by using wireline in coiled tubing: installing the wireline in the coiled tubing, attaching sensor or apparatus or wireline tools comprising the sensor or apparatus to the downhole end of the coiled tubing string, taking and recording measurements, and later analyzing the recorded information to improve or optimize the next coiled tubing operation. Coiled tubing operations would be improved if downhole measurement data were available in real time while the operations were ongoing. In this regard, fiber optics are known to be useful in providing measurement data in real time.
U.S. Pat. No. 6,531,964, incorporated herein in its entirety by reference, describes use of fiber optic sensors to make measurements of downhole conditions in a borehole. A method is presented for deploying fiber optic devices into a wellbore include pumping the devices under pressure using a fluid. Another method for deploying a production or completion string into a borehole is also provided, the string including a hydraulically operable device carried by a tubing. A fluid conduit is provided either outside or inside the string and a hydraulic connection is provided from the fluid conduit to the hydraulically operable device so that fluid under pressure can pass from the conduit to the device. After the string has been installed to the desired depth in the wellbore, then an optical fiber can be pumped into the conduit, the conduit having a U-shaped component to permit the leading end of the optical fiber to return to the surface. Disadvantages of this method include the need for providing a separate conduit for single optical fiber installation. Furthermore, the requirement of this configuration that a conduit is provided in the initial installation limits operational flexibility; this limitation is addressed by the present invention.
Thus, the prior art with respect to deploying cable into coiled tubing teaches methods to install cable into coiled tubing using mechanical means to overcome the pressure differential encountered when deploying coiled tubing into a borehole or using a combination of configured flow tubes and fluid flow to overcome the pressure differential. The prior art with respect to deploying optical fibers in a borehole teaches the need for fluid conduit into which the optical fiber is deployed and the pressured fluid pumped. There remains a need for a method and apparatus for deploying a line in coiled tubing that overcomes the resistance to insertion caused by the wellbore pressure and does not require a separate conduit. The present invention addresses shortcomings in the prior art. The issues that have affected the use and industry's ability to implement wireline in particular and lines in general in coiled tubing operations are addressed by the present methods and apparatus for deploying a line in coiled tubing.